The need for data reduction, e.g. to represent digital data by using fewer bits, has become a recognized objective in several fields, e.g., communication and data storage. Considering a specific example, conventional teletype systems operate utilizing binary signals to represent seven-bit codes, each seven-bit code group identifying one of 128 possible characters. In using such a code, conventional representation of a message requires a number of bits equal to the number of characters (in the message) multiplied by seven. For example, the representation of a 196 character message would require 1,372 bits.
The invention disclosed herein provides both a method and an apparatus for shortening such conventional message formats. However, the system of the present invention is applicable generally for the registration or transmission of various digitized messages such as may occur in teletype, television, telephony, telemetry, and so on.
In the system of the present invention, reducing the transmitted or stored binary data is accomplished by formatting or dividing a message into data blocks or sequences of characters (alpha-numeric, for example), each of which contains a predetermined number of binary-coded characters. The block is then analyzed by a dissection philosophy that involves priority treatment of characters. Advantage is taken of the fact that most intelligence-bearing messages have some degree of coherency (certain elements or characters of the message are repeated within the data block more often than others). That is, a coherent data block normally includes several characters that are variously repeated while some characters may not be present at all. By identifying the characters used in a data block, treating them in limited sets, e.g. four characters, and assigning abbreviated codes while specifying their locations in the data block, the representative binary format may be reduced. Other aspects will become apparent as treated below in detail.